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<title>Issue 3279: shared_ptr&lt;int&gt;&amp; does not not satisfy readable</title>
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<p><em>This page is a snapshot from the LWG issues list, see the <a href="lwg-active.html">Library Active Issues List</a> for more information and the meaning of <a href="lwg-active.html#Resolved">Resolved</a> status.</em></p>
<h3 id="3279"><a href="lwg-defects.html#3279">3279</a>. <code>shared_ptr&lt;int&gt;&amp;</code> does not not satisfy <code>readable</code></h3>
<p><b>Section:</b> 24.3.4.2 <a href="https://wg21.link/iterator.concept.readable">[iterator.concept.readable]</a> <b>Status:</b> <a href="lwg-active.html#Resolved">Resolved</a>
 <b>Submitter:</b> Eric Niebler <b>Opened:</b> 2019-09-09 <b>Last modified:</b> 2020-09-06</p>
<p><b>Priority: </b>1
</p>
<p><b>View all issues with</b> <a href="lwg-status.html#Resolved">Resolved</a> status.</p>
<p><b>Discussion:</b></p>
<p>
In the current spec, <code>shared_ptr&lt;int&gt;</code> is <code>readable</code>, but <code>shared_ptr&lt;int&gt;&amp;</code> 
is not. That is because <code>readable_traits</code> is not stripping top-level references before testing 
for nested typedefs.
<p/>
Either <code>readable_traits</code> should see through <i>cv</i>- and ref-qualifiers, or else the 
<code>readable</code> concept should strip top-level references when building the <code>iter_value_t</code> 
associated type (e.g., <code>iter_value_t&lt;remove_reference_t&lt;In&gt;&gt;</code>).
<p/>
Suggest priority P1 because it effects the definition of a concept which cannot change after C++20.
</p>
<p><i>[2019-10 Priority set to 1 after reflector discussion]</i></p>

<p><i>[2019-11 This should be resolved by <a href="https://wg21.link/P1878">P1878</a>]</i></p>


<p><strong>Previous resolution [SUPERSEDED]:</strong></p>
<blockquote class="note">
<p>This wording is relative to <a href="https://wg21.link/n4830">N4830</a>.</p>

<ol>
<li><p>Modify 24.3.4.2 <a href="https://wg21.link/iterator.concept.readable">[iterator.concept.readable]</a>, concept <code>readable</code> synopsis, as indicated:</p>

<blockquote>
<pre>
template&lt;class In&gt;
  concept readable =
    requires {
      typename iter_value_t&lt;<ins>remove_reference_t&lt;</ins>In<ins>&gt;</ins>&gt;;
      typename iter_reference_t&lt;In&gt;;
      typename iter_rvalue_reference_t&lt;In&gt;;
    } &amp;&amp;
    common_reference_with&lt;iter_reference_t&lt;In&gt;&amp;&amp;, iter_value_t&lt;<ins>remove_reference_t&lt;</ins>In<ins>&gt;</ins>&gt;&amp;&gt; &amp;&amp;
    common_reference_with&lt;iter_reference_t&lt;In&gt;&amp;&amp;, iter_rvalue_reference_t&lt;In&gt;&amp;&amp;&gt; &amp;&amp;
    common_reference_with&lt;iter_rvalue_reference_t&lt;In&gt;&amp;&amp;, const iter_value_t&lt;<ins>remove_reference_t&lt;</ins>In<ins>&gt;</ins>&gt;&amp;&gt;;
</pre>
</blockquote>
</li>
</ol>
</blockquote>

<p><i>[2019-11; Resolved by the adoption of <a href="https://wg21.link/P1878">P1878</a> in Belfast]</i></p>



<p id="res-3279"><b>Proposed resolution:</b></p>
<p>
Resolved by <a href="https://wg21.link/P1878">P1878</a>.
</p>




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